This invention relates generally to rotating electrical machines, and more particularly to rotating starting resistances for electrical machines, which rotate with the rotating member of the electrical machine.
Rotating starting resistances, which are connected in a series or field circuit to modify the starting performance of electrical machines, are known in the art. See, for example, "Brown Boveri Mitteilungen" [Brown Boveri Reports], Volume 54, No. 9, at page 550, and "Dreiphasen-Synchronmotoren Typ WM 400 . . . 1000 4-Bis 14 Polig" [Three-Phase Synchronous Motors, Type WM 400 . . . 1000 4-to 14 Pole], CH-T5432, BBC Aktiengesellschaft Brown, Boveri & Cie., Baden, Switzerland, FIG. 8b at page 12.
A conventional starting resistance is manufactured in the form of a coiled strap of resistance material, such as steel or German silver. The coiled strap is then insulated with an insulating strip. This form of resistance, however, cannot be effectively cooled due to the insulation. Moreover, this type of construction requires the starting resistance to have a relatively large overall height.
It is therefore an object of this invention to provide a rotating starting resistance for an electrical machine which can be more effectively cooled, and which has a relatively smaller overall height than conventional rotating starting resistances.
According to a preferred embodiment of the present invention, the starting resistance is constructed from a helicoidal winding of resistance wire which is wound in the shape of a torus. The starting resistance is then mechanically connected to the rotating shaft of the electrical machine by suitable supporting elements. The resistance wire can be made from such materials as steel, German silver or a nickelchromium alloy.
The helicoidal nature of the resistance wire used to form the starting resistance allows effective cooling of the resistance, and allows a resistance of a given resistance value and thermal capacity to be constructed having a minimum overall height.